1. Field of the Invention
The present invention relates generally to antenna related technologies, especially an antenna capable of supporting multi-band communications.
2. Description of the Related Art
The development of wireless communication systems and devices has increased dramatically over recent years. Various products and techniques have been developed to support multi-band communications to meet increasing consumer demands. For example, some laptop computers or mobile phones equipped with wireless capabilities can now receive and display digital signals typically for digital televisions.
Such digital television signals are subject to regulations. For example, the frequency range for the digital television signals, as regulated by the Digital Video Broadcast (DVB) consortium, is from 470-860 MHz. This frequency range however differs from the frequency (e.g., 2.45 GHz) used by other wireless applications, such as WiFi and Bluetooth, that may be supported by the same laptop computers or mobile phones. To support a wide range of frequencies, traditional design approaches may involve multiple antennas.
Conventional antennas generally adapted in wireless communication systems and devices are grouped into two types, monopole antennas and dipole antennas. A monopole antenna typically has a simple structure and covers a wide range of frequencies, but requires a considerably wide ground plane to achieve the desired radiation efficiency. In addition, a monopole antenna is best used for a specific frequency band, such as the frequency band for devices operating according to the Code Division Multiple Access (CDMA) protocol or the frequency band for devices operating according to the Global System for Mobile communications (GSM) protocol.
A dipole antenna generally includes a pair of wires and is driven by a voltage signal applied to the center of the antenna. The dipole antenna effectively radiates and receives electromagnetic waves and is used in various communication fields. For the conventional dipole antenna to maintain optimal polarization effects, its dimension cannot be effectively reduced. Similar to the monopole antenna discussed above, the dipole antenna is also best suited to operate in a single frequency band.
As has been discussed, both the conventional monopole antenna and the conventional dipole antenna need to maintain certain sizes to achieve desirable effects. Furthermore, to cover a wide range of frequencies, an antenna including multiple antenna elements, each of which is responsible for a particular frequency range, is typically used. With the multiple antenna elements and some required distance to separate among the antenna elements, reducing the size of the antenna becomes challenging. Also, some signal control may be required in each of the antenna elements, which complicates communication processing and causes an increase in power consumption. Some other problems associated with using multiple antenna elements include the difficulty of mounting the antenna elements and the potential interferences among the antenna elements.
Hence, it is expected that an antenna only operating in a single frequency band is not a cost-effective solution, especially with a wireless communication system and device continuing to be miniaturized. Therefore, what is needed in the art is an antenna capable of supporting multi-frequency communications and addresses at least the problems set forth above.